Mitt Romney's marginal primary victory in the Michigan has turned out to be a dead heat after the final count showed rival Rick Santorum still won half the state's delegates.

Romney's result in the state of his birth lost some of its lustre as it emerged he and Rick Santorum each received 15 delegates. The result, despite Romney winning 41% of the primary vote compared with Santorum's 38%, came about because Michigan divides up delegates on a proportional basis.

The outcome muddies the race ahead of 10 key state contests next Tuesday.

A win in Michigan had been crucial for Romney, whose father was governor of the state. He had aimed to overcome the religious conservative Santorum by sticking to his core and mainstream Republican message of fixing the economy and reducing unemployment in a country still recovering from the worst recession in decades.

News that Santorum's narrow loss in Michigan would yield him as many delegates as the winner enabled him to label the result a success on Romney's home turf, putting some wind in his sails ahead of the big contests next week.

"We had a much better night in Michigan than maybe was first reported. This was a really great race to go into, in a sense, the belly of the beast, the hometown of my chief rival here in the Republican primary," Santorum said during a campaign stop in Tennessee.

The other two candidates in the race, Newt Gingrich and Ron Paul, did not campaign in Michigan and got no delegates.

On Wednesday night Romney won his party's caucus in Wyoming, CNN reported, quoting the Wyoming Republican party as saying Romney emerged from a month-long series of county-level straw polls with 39% of the votes cast.

The TV network said former Santorum came in second with 33%, followed by Ron Paul with 20% and Newt Gingrich with 8%.

Romney is favoured by much of the Republican establishment and enjoys more campaign funds and better organisation than his primary rivals. But Santorum has electrified the party's conservative base, which trusts his views on social issues such as abortion and gay rights, and considers Romney too moderate and inconsistent.

Santorum remains on solid ground heading into Super Tuesday, when 419 delegates are up for grabs in 10 states. It could go a long way in determining who will win the state-by-state race for delegates that yields the party's nomination at its national convention in August.

Santorum is leading the polls in Ohio, possibly the most important contest on Super Tuesday. It is a big industrial state with 8.1% unemployment, 63 convention delegates at stake and a long history as a battleground in general election campaigns. Santorum also is keeping an eye on two other big prizes among the 10 Super Tuesday states: Oklahoma and Tennessee.

Romney is all but assured of victories in at least two of next Tuesday's states - Massachusetts, where he was governor and faces little or no competition in the primary, and Virginia, where neither former House speaker Newt Gingrich nor Santorum qualified for the ballot. Those two contests offer 84 delegates combined.

• This article was amended on 5 March 2012. The original sub-heading referred to Mitt Romney winning a majority of votes. This has been corrected.